1. Field of the Invention
This invention is directed to a system for the thermal and/or liquid treatment of edge supported substrates, such as printed electronic circuit boards and the like, and especially as applied to surface mount technology. More particularly, the invention is directed to a novel lubricant-free flexible steel tape conveyor having projecting tabs providing lateral support for the circuit boards or hybrid circuits or similar substrates suspended between the tapes by their edges in the course of passage through thermal and/or liquid treatment.
In the manufacture of printed circuit boards or hybrid circuits, it is common practice to subject the boards to successive liquid and thermal treatment steps including solvent degreasing, spray coating, drying, baking, and the like. Such treatments are difficult to carry out on a continuous basis utilizing available conveyor systems since the treatments have a deleterious effect on the conveyor systems, as by removing lubricant, baking and solidifying lubricant, and the like. The present invention is directed toward alleviation of the deficiencies of the prior art.
2. The Prior Art
According to current practice, circuit boards are transported through treating chambers by means of full product width wire mesh conveyor belts or roller-type chain conveyors. The successive hubs of a roller chain are provided with projecting pins. Panels to be treated are supported on those pins between a pair of chains and carried through a treating chamber. Such conveyors tend to fail through loss of lubricant in solvent degreasing treatments, by congealing of the lubricant in heating treatments, and the like.
In my aforesaid copending application Ser. No. 840,311, there is disclosed a system for the thermal and/or liquid treatment of edge supported substrates alleviating the problems of the prior art. The system includes an elongated tunnel treating chamber provided with elements for liquid and/or thermal treatment of substrates carried through the treating chamber. The conveyor system for transporting material through the treating chamber includes a pair of elongated rail tracks extending through the treating chamber. These rail tracks are supported by members disposed outside of the treating chamber at the opposite ends of the chamber. A lubricant-free flexible steel tape conveyor is provided on each rail track. Each tape is provided with a plurality of longitudinally spaced apart vertical tabs throughout its length. The tabs are in longitudinal alignment, spaced inwardly from the edges of the tape and provide lateral support for substrates suspended between the pair of conveyor tapes. Means are provided for moving the conveyor along the rail tracks through the treating chamber.
In the system of my aforesaid application, the tape conveyor travels through the treating chamber with the bottom surface of the tape in face-to-face sliding contact with the upper surface of the supporting rail track. When the system is used for thermal treatment of substrates, after prolonged heating the rail track may become excessively hot. This may cause buckling and warping of the conveyor tape.